Insight into the Controlled Synthesis of Cu2Zn(Ge,Sn)S4 Nanoparticles with Selective Grain Size

Controlled synthesis of absorber materials Cu2ZnGeS4 (CZGS) has been performed using different Ge precursors, including GeCl4 and the self-synthesized Ge complexes with Ge-glycolic acid (denoted as Ge-Gly), Ge-tartaric acid (denoted as Ge-Tar), and Ge-citric acid (denoted as Ge-Cit). The grain size of as-prepared CZGS nanocrystals (NCs) is dependent on the Ge precursors. All four Ge precursors enabled the wurtzstannite CZGS phase formation. The Ge-Cit precursor led to the formation of monodispersed NCs owing to the fact that the undissolved metal-Cit complex in OLA absorbed the small CZSG NCs and avoided the irregular crystalline behavior. The other three precursors induced two different sizes, and the corresponding reaction mechanism has been proposed. Moreover, the Cu2ZnGe1–xSnxS4 NCs with different Ge/Sn ratios were prepared using the Ge-Cit precursor, verifying the general effect on the phase formation and selective grain sizes. The compositional effect on the band gap variation and morphologies of Cu2ZnGe1–xSnxS4 was also studied.